The accurate measurement of natural gas and other fluids is of critical concern. The measurement of natural gas and other fluids is required with the production, processing, transportation and distribution of natural gas and fluid products from exploration to utilization. The accurate measurement of fluids having a substantial monetary value, for example, natural gas, natural gas liquids, hydrocarbon gases, hydrocarbon liquids, and the like, is essential to the efficient use of the fluids and controlled cost accounting. Specifically, the accurate measurement of fluids is essential for determining accountable custody transfer determinations.
Pipelines are used to transport fluids such as the production fluids from oil and gas wells, natural gas, natural gas liquids, hydrocarbon gases, hydrocarbon liquids, and the like. The accurate measurement of these fluids is unquestionably important. Instruments are required to accurately measure such fluids in pipelines. Orifice plates are a well known device for assisting in the measurement of such fluids. Orifice plates are installed in special fittings, and the fittings are installed in-line with pipeline sections. An example of such a special fitting is the Daniel.RTM. Senior.RTM. orifice fitting. The term Senior.RTM. as applied to orifice fittings specifically denotes a dual-chamber orifice fitting. Such dual-chamber orifice fittings provide a fast, safe and extremely simple method of changing orifice plates under pressure without interrupting the flow of fluid. The dual-chamber orifice fitting holds the orifice plate in the fluid flow stream, or alternately, the orifice plate is displaced from the fluid flow stream without interrupting the flow of fluid through the pipeline. For example, the Daniel.RTM. Senior.RTM. orifice fitting has been adapted for use with pipeline sizes from approximately 2 inches to 48 inches, and having a pressure rating of up to 10,000 pounds per square inch. Alternate techniques include interrupting the flow, using costly by-pass equipment, or using valve systems and other fittings required with conventional orifice flange installations.
To permit an orifice plate to be lowered into the pipeline flow using a dual-chamber orifice fitting, valves are located in the fitting to selectively seal and unseal a lower chamber from an upper chamber. The valves can be any of various devices that regulate the flow of gases or liquids through the pipeline, piping or through related apertures by opening, closing, or obstructing ports or passageways. Such valves typically comprise a stainless steel valve strip, or rectangular bar, which is manipulated by a valve carrier engaged with a drive mechanism such as a rack and pinion gear. The valve strip covers the aperture between the lower and upper chambers and is biased against the aperture by springs and by the pressure of the fluid in the pipeline and lower chamber. To effectively seal between the valve strip and the seat attached to the orifice fitting surface which surrounds the aperture, typically, a chemical or petroleum based lubricant is injected through passageways and grooves to seal the joint between the valve strip and the orifice fitting.
To remove the orifice plate from the pipeline using the dual-chamber orifice fitting, a valve strip carrier is operated to move the valve strip away from the aperture, and the orifice plate is then mechanically moved through the aperture from the lower chamber to the upper chamber. The valve strip carrier is then operated to move the valve strip back into position such that it covers the aperture to prevent fluids in the lower chamber from passing to the upper chamber. The upper chamber is then vented and the orifice plate can be removed.
In certain pipeline applications, the slide valve presently used to seal the aperture may not be desirable. Such a condition may exist if the lubricant is not compatible with the pipeline fluid or if an absolute seal is required, particularly at extremely low pipeline pressures. There is a need for a slide valve which does not utilize lubricants and which creates an absolute seal at any pipeline pressure.
Of concern in the present invention is to remove or change orifice plates under pressure without interrupting the flow of fluid. It is, therefore, a feature of the present invention to provide a sealing apparatus for sealing the aperture located between the first and second chambers of an orifice fitting.
A feature of the present invention is to provide a sealing apparatus having a positive engagement assembly.
Another feature of the present invention is to provide a sealing apparatus which can be operated in association with a dual-chamber orifice fitting regardless of the orientation of the fitting.
Another feature of the present invention is to provide a sealing apparatus where the disparity between lubricant and pipeline fluid is not a problem.
A further feature of the present invention is to provide a sealing apparatus where an absolute seal is required.
Yet another feature of the present invention is to provide a sealing apparatus adaptable for extremely low pipeline pressures.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.